Recently, mobile telephone services were introduced wherein a subscriber only needs one single mobile phone that is suitable for calling via Voice Over IP (VOIP) and via GSM/UMTS. If the subscriber resides at home, she may call via a radio based connection like Wireless Local Area Network (WLAN), Wireless Fidelity (WIFI), or Bluetooth. These radio based connections are collectively denoted as UMA (Unlicensed Mobile Access). GSM, UMTS and the like are denoted as GAN (Global Access Networks). Phones capable of connection in both UMA and GAN are denoted as UMA/GAN phones. For a subscriber to use the phones capabilities she needs to have either GAN and UMA subscriptions or a combined UMA/GAN subscription. Below, it is assumed that a subscriber has a combined UMA/GAN subscription. Such a subscriber is simply referred to as a UMA-subscriber.
In co-pending patent application PCT/NL2006/050279 a method of routing a call made by a calling party to a fixed telephone number of a called party is described. The call is routed to a mobile terminal via an Internet Protocol (IP) network and a WLAN access point (AP) associated with the fixed telephone number only when the mobile terminal is located in an area covered by the WLAN AP. The call is routed to an alternative terminating point, such as a voicemail system, if the mobile terminal is located outside the WLAN coverage area. The basic idea of PCT/NL2006/050279 is to provide subscribers with a fixed telephone number the facility to route calls that are made to the fixed telephone number either to a mobile phone of the subscribers when they are located in a so-called ‘Home Zone’, or else to an alternative terminating point, such as a voice mail of the subscriber that may reside in the telecommunication network of a telecom provider. A Home Zone is determined by an area which is covered by one or more wireless access points. The service which is provided to the subscribers is also referred to as the ‘@home service’.
In publication EP 1.804.435 A1 a method is described wherein a call to a UMA-subscriber is routed depending on the UMA-subscriber being “at home” or “not at home”. The Home Zone in EP 1.804.435 A1 is defined as being a set of GSM cells or a set of distributed WLAN AP. The Home Zone is a low fee area in which the UMA-subscribe may receive calls from a calling party in which case, the latter pays a lower fee than usual.